Mine roof supports



g- 5, 1970 K. G. HANCOCK ET AL 3,525,227

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United States Patent 3,525,227 MINE ROOF SUPPORTS Kenneth GeorgeHancock, Lower Walton, Warrington, Peter Frank Eastwood, Grappenhall,Warrington, Brian Worrall, Clock Face, near Bold, St. Helens, and RonaldRoy Reeves, Great Sankey, Warrington, England, assignors, by mesneassignments, to Gullick Limited, Wigan, Lancashire, England Filed July19, 1968, Ser. No. 746,070 Claims priority, application Great Britain,July 19, 1967, 33,218/67; Aug. 21, 1967, 38,509/67 Int. Cl. E2111 23/00US. Cl. 61-45 8 Claims ABSTRACT OF THE DISCLOSURE Mine roof supports ofthe advancing type comprise one or more roof contacting members, one ormore floor contacting members with one or more props arrangedtherebetween and having two laterally spaced apart support advancingrams pivotally connected to the support and adapted for connection to ananchorage, for example a coalface conveyor. Guide surfaces are providedon the support to co-operate with complementary first surfaces carriedby adjacent supports, or co-operating first surfaces carried byindependently movable parts of the same support, whereby duringadvancing movement of the support it is guided relative to an adjacentroof supporting member or members.

This invention, relates to advancing mine roof supports of the typecomprising one or more roof contacting members, one or more floorcontacting members with one or more props arranged therebetween andhaving two laterally spaced apart support advancing rams pivotallyconnected to the support and adapted for connection to an anchorage, forexample a coalface conveyer. More particularly the invention concernsthe guidance of such a support during its advancing movement.

The advancing rams referred to may be single acting and used to advancethe support to the conveyer or they may be double acting. In the lattercase they may be used to advance the conveyor when the support is set tothe roof and subsequently (the conveyer being retained in its advancedposition by adjacent supports), used to advance the support, after itsrelease from supporting the roof, up to the conveyor. Longitudinalmovement of the conveyer frequently occurs during its advancement andprovision for this must be made in the manner in which the advancingrams are connected between the conveyer and the support; otherwise therams will be damaged, for example by bending of their piston rods.Provision should also be made to ensure that when the support isadvanced it takes up a position normal to the conveyer. A number ofproposals have been made for guiding the advancing movement of thesupport over at least a part of its travel into a position normal to theconveyer, such guidance being provided from a member or membersconnected to the conveyer. However these proposals rely on there beingno obstruction to the advance of the support so that both rams operategenerally in synchronism. In practice advance of the support is notinfrequently partially obstructed so that one ram closes whilst theother cannot do so and due to this the support is twisted round to such3,525,227 Patented Aug. 25, 1970 "ice a degree that one or other of therams fouls the support and is damaged, usually by bending of the pistonrod. The purpose of this invention is to provide a mine roof support inwhich this problem is overcome.

SUMMARY OF THE INVENTION According to the present invention a mine roofsupport of the type described comprises first guide surfaces carried bythe support and adapted to co-operate with complementary first surfacescarried by adjacent supports, or co-operating first surfaces carried byindependently movable parts of the same support, whereby the support, orthat part thereof to which the aforementioned rams are connected, isguided relative to an adjacent roof supporting member or members over asubstantial part of the support advancing stroke of the rams and therestraint imposed by the co-operating guide surfaces is removed over thefinal advancing movement of the support so as then to permit lateralmovement thereof.

Preferably the first guide surfaces carried by the support compriseforward and rear sections providing discontinuous guide surfaces.

Preferably the connection of the rams to the anchorage comprises linkmembers pivotally connected to the rams and adapted for pivotalconnection to the anchorage, each link member having a second guidesurface arranged to co-operate with a second surface on the support soas to guide the support into a predetermined position relative to theanchorage during closure of the rams, the link members being so formedand the pivotal connections between the anchorage, the link members andthe rams being so arranged that, when the support approaches its fullyadvanced position, the axis of each ram is inclined to a line joiningthe pivotal connections at the anchorage and the support, whereby aleverage is exerted on the link members tending to exert a lateral forceon the support so as to steer it into a predetermined positlon relativeto the anchorage or restrain it from moving away from that position.

Preferably the second guide surface on each link member is formed with aprojection cam or the like beyond which the leading edge of theco-operating second surface on the support passes, when the support isfully advanced to the anchorage, so that the support is guided orsteered into its predetermined position even though it may not be fullyadvanced to the anchorage.

Preferably the connections of the link members to the anchorage arearranged to permit relative vertical movement.

The link members may be provided with abutment surfaces for engagementwith the anchorage so that, when double acting rams are provided, theanchorage may be advanced thereby.

Means may be provided to prevent overlapping of link members of adjacentsupports, for example, during lateral movement of the anchorage relativeto the supports. I

The invention is described by way of example only With reference to thedrawings in which:

FIGS. 1(1) (A), 1(I)(B), 1(II) (C) and 1(II) (D) show diagrammaticallyin plan successive positions of the parts in the advance of a mine roofsupport;

FIG. 2 is a diagrammatic scrap view in plan illustrating one method ofconnecting an advancing ram to an anchorage, e.g. a coalface conveyor;

FIG. 3 is a diagrammatic plan view showing in part only one ram, apreferred link member, the co-operating second surface of a support andan anchorage;

FIG. 4 is an elevation showing the connections between the ram, linkmember and anchorage of FIG. 3;

FIGS. 5(I) (A), 5(I) (B), 5(II) (C), and 5(II) (D) show diagrammaticallyin plan successive positions of the parts in the advance of a mine roofsupport; and,

FIGS. 1(I) (A)-1(II)-(D) are referred to collectively in some instancesin the following descriptions as FIG. 1; and, FIGS. 5(1) (A)-5(II) (D)are referred to collectively in some instances as FIG. .5; and,

FIG. 6 is a fragmentary perspective view of two outer support elementsand an inner or third support element, showing cooperating guidesurfaces on the support elements.

Referring to FIGS. 1 and 5, a composite mine roof support is shown whichconsists of two outer support elements 2, 3 in conjunction with an inneror third roof support element 4. The elements 2, 3 are similar and eachhas a base 5A, 5B, two hydraulically operated telescopic props 6A, 7A,6B, 7B, resiliently mounted thereon and a roof contacting member in theform of a roof bar 8A, 8B respectively carried by the props in knownarticulated manner, Brackets 9, 10 are secured to the rear ends of thebases 5A, 5B respectively. The bases 5A, 5B are connected together by asubstantial metal plate 11 having side lugs 12 which span the brackets9, 10 and are connected to them by transversely disposed pins 13, thelatter being located by split pins (not shown).

First and second double acting advancing rams 35, 36 have their pistonrods pivotally connected to brackets 17 on the bases 5A, 5B and theircylinders are pivotally connected to links 38 (FIG. 1), 95 (FIG. 5)which are in turn pivotally connected to a conveyor 30, all the pivotaxes being in the vertical plane.

The third roof of support element 4 comprises a base '41, twohydraulically operated props 43., 44 resiliently mounted thereon and aroof bar 42 carried by the props in known articulated manner. The base41 has sideways clearance (see position D) between the bases 5A, 5B theamount of clearance provided on either side being not less than themaximum anticipated longitudinal movement of the conveyor 30 during onecycle of advance.

The cylinder of a third advancing ram 45 has a horizontal pivotconnection to the base 41 and its piston rod has a vertical pivotconnection at 67 to a lever 68 intermediate the ends thereof. The endsof the lever 68 have vertical pivot connections at 69, 70 to the rearends of two members 71, 72 whose forward ends, cranked at a small angle,are horizontally pivotally connected at 73, 74 to the inwardly facingsides of the bases 5A, 5B of the elements 2 and 3 respectively.

The roof bar 42 comprises a rigid main portion 58 to which is bolted anarrower front portion 59 in the form of a leaf spring.

Plates 53A, 54A (FIG. 1) bolted to the bases 5A, 5B have tapered edges55, 56 which comprise first guide surfaces which co-operate withcomplementary first surfaces on the third roof support element 4 wherebythe outer elements 2, 3 of the support are guided over a substantialpart of the support advancing stroke of the rams 35, 36. As shown inFIG. 6, the complementary first surfaces are constituted by an upwardlyinclined plate 140 at the front end of the base 41 and a generallyvertical plate 141 on each side which is joined to the upwardly inclinedplate 140.

Referring now to FIG. 2 each link 38 comprises similar upper and lowerlink portions (the lower being masked in the drawing by the upper)having a common vertical pivot connection 90 to the conveyor 30 and theyare arranged above and below a thrust member 91 which comprises anextension on the ram cylinder towards the conveyor 30. The thrust member91 is slotted at 92 and a pin 93 passes through the link portions andthe slot 92. The length of the slot 92 is such that on extension of theram the free end 94 of the thrust member 91 engages a thrust plate orthe like (not shown) on the conveyor 30 leaving clearance between theend of the slot 92 remote from the conveyor 30 and the pin 93.

Referring to FIG. 5, similar, but shorter, forward plates 53A, 54A areprovided on the bases 5A, 5B of the support of FIG. 5. The plates 53Aare respectively formed with guide surfaces 53B, 55 and 54B, 56. Rearplates 105, 106 are also provided, bolted to the bases 5A, 5B towardstheir rear ends, at such a height that they are clear of the uppersurface of the base 41, each being provided with guide surfaces (forminga part of the first guides) 107, 108, 109, 110 similar to the surfaces53B, 55 and 54B, 56 provided on the plates 53A, 54A. Two bearing pads111, 112 are mounted on a cross member 113 above the rear end of thebase 41 in the way of the plates 105, 106 (positions A and B) whichco-operate with the surfaces 107, 108, 109, 110.

Referring now to FIG. 3 the cylinder of the ram 36 is pivotallyconnected at 95A to one end of a link 95 whose other end is pivotallyconnected at 95B to a bracket 96 which is secured as by bolts and nutsto a coalface conveyor 30. The link 95 has at its forward end twosurfaces 97, 98 inclined at an angle to one another, which define limitsof angular movement of the link 95 relative to the conveyer 30 byabutment with the bracket 96. As shown, the surface 97 is abutting thebracket 96 and thereby limiting angular movement of the ram 36 away fromthe "base 5B. In this position the line of action of the ram 36 is shownat 99 and its lever arm about the pivot 95B is shown at 100. The link 95is provided with a second guide surface 101 culminating in a projectionor cam 102 which guide surface and cam are adapted to co-operate with asecond surface on the support which may conveniently be a verticalsurface extending rearwardly from a forward location 103 on the base 5B.The link may also include vertical surfaces 104 at its side remote fromthe support, seen more clearly in FIG. 4, for a purpose to be described.Also depicted in FIG. 3, in chain dotted lines, is the position of theram 36, link 95 and base 5B when the support has been fully advanced tothe conveyor 30 and guided--in a manner to be describedinto apredetermined position relative to the conveyor 30. In this position thesurface 98 on the link 95 abuts the bracket 96 and the cam 102 mayengage the co-operating second surface on the support or may have asmall clearance therefrom. The line of action of the ram 36 has nowmoved to 99A whilst the length of the lever arm has reduced from thatshown at to that shown at 100A, and it will be seen that the line ofaction of the ram, which lies along its axis, is inclined to a linejoining its rear pivotal connection to the support (at bracket 17) (FIG.5) and the pivotal connection at 953 of the link 95 to the conveyor 30.A leverage is thus exerted on the link 95 which, if its surface 98 hasnot yet abutted the bracket 96, imparts a lateral force on the supportto steer it towards its final predetermined position as the ram 36approaches its fully closed position. When the surface 98 does abut thebracket 96 the leverage exerted on the link 95 now acts to restrainmovement of the support from its predetermined position. There is alsoshown in chain dotted lines part of the ram and link of an adjacentsupport, to which further reference will be made later.

Referring now to FIG. 4 which includes an elevation of the bracket 96 itwill be seen that in the way of the pivot 95B the bracket is formed as ayoke the upper and lower arms of which are spaced apart to permitrelative vertical movement between the link 95 and the conveyor 30.

Referring again to FIG. 1 and 5, in position A the roof support is shownready to advance the conveyor 30 into a position adjacent a new coalface62 exposed by the passage of a coal cutting machine (not shown). Thisadvance of the conveyor is shown as having taken place in position B.The advance is effected by extension of the rams 35, 36. Initialmovement of the rams causes thrust members 91 (FIGS. 1 and 2) to engagethe conveyor 30 whereby the force exerted by the rams is transmitteddirect to the conveyor 30 and not through the pins 90, 93. In the caseof the support of FIGS. 3 to 5 initial extension of the rams 35, 36causes rotation of the links 95 so that their surfaces 97 abut thebrackets 96 and the cams 102 move away from the bases 5A, 5B. The forceexerted by the rams 35, 36 is transmitted to the conveyor 30 via thelinks 95 and brackets 96. Longidinal or endwise movement of the conveyor30 can be accommodated by pivotal movement of the links 38, 95 and therams 35, 36. During this operation the roof bars 8A, 8B and 42 will beset in roof supporting position.

Following the advance of the conveyor 30 and its retention in theadvanced position by adjacent supports, the elements 2, 3 of thecomposite support are released from supporting the roof and the rams 35,36 are closed so as to advance the elements 2, 3 to a position adjacentto the conveyor again. Due to the tension force in the rams 35, 36 andthe links 38, 95 the support elements 2, 3 will tend to be advanced intoa position normal to the conveyor 30. It will be noted (FIG. 5B) thatbefore advancement of the elements 2, 3 the links 95 are well forwardand clear of the second surfaces on the bases 5A, 5B so the tensionforce in the rams will rotate the links 95 so that their surfaces 98abut the brackets 96, as shown in FIG. 5B. It will of course be clearthat the rams, the links and their connections to the support and theconveyor are so arranged that the rams have clearance from the bases ofthe support in this position even though the maximum anticipatedmovement of the conveyor transversely of the support has taken place.Such movement will bring the cylinder end of one of the rams towards itsassociated base and the other will be moved so that it has additionalclearance from its associated base.

The support elements 2, 3 will now be drawn forward and FIGS. 1C and 5Cshow them partially advanced. Their path of advancement will be definedby the orientation of the third roof support element 4, which ismaintained in roof supporting position, due to the first surfaces on thebase 41 co-operating with the first guide surfaces. That is to say, thefirst surfaces on the base 41 co-operate with the plates 53A, 54A (FIGS.1 and 5) and the pads 111, 112 co-operate with the plates 105, 106 (FIG.5). When the surfaces 108, 110 on plates 105, 106 have moved forward andclear of the pads 111, 112 guidance at the rear end is maintained for afurther distance by cooperation of the surfaces 108, 110 with theupstanding sides of the mounting for the prop 43 as is shown in FIG. 5C.7

If closure of one or other of the rams 35, 36 is prevented, for exampledue to an obstruction between the base 5A and the conveyor 30, theelements 2, 3 are prevented from twisting round due to closure of theram 36 by interaction of the guide surfaces which have been describedprovided between the bases 5A, 5B and the element 4. The amount to whichelements 2, 3 can be twisted is limited by the clearance between theco-operating guide surfaces and the degree of twist permitted isarranged to be less than that which is required to cause either of therams 35, 36 to foul their respective support elements 2, 3 for example,when the maximum movement of the conveyor transverse to the support hastaken place. Thus in this condition if the obstruction is not cleared bythe pull of the rams 35, 36 the advancing movement of the elements 2, 3is stalled and action must then be taken to clear the obstruction toenable advance of the elements 2, 3 to be completed.

Referring now to the position (D) it will be seen that as the elements2, 3 approach their fully advanced position, the first guide surfaces53B, 54B and 108, 110 (FIG. 5) move clear of the co-operating firstsurfaces on the element 4 so as to permit lateral movement of theelements 2, 3 and permit any necessary re-alignment of the elements 2, 3with the conveyor 30. Guide plates (not shown) may be provided ifdesired on the conveyor 30 to engage bases 5A, SE to guide the elements2, 3 into contact alignment with the conveyor 30 during the final stagesof their advancing movement and after release of the restraint tolateral movement of the elements 2, 3. Alternatively this guidance maybe provided by suitable shaping of the links 38, for example as shown atin FIGS. 3 to 5.

It will thus be seen that the possibility of damage to the advancingrams is obviated by guiding the advancing movement of a support byreference to the orientation of an adjacent roof support member untilthe advancing support is close to the conveyor at which stage lateralmovement of the support is permitted so that it can then move laterallyrelative to the conveyor and, if necessary, be guided relative thereto.

One manner in which the support, namely the elements 2, 3 in thisembodiment, can be guided into a predetermined position relative to theconveyor will now be described. Referring to FIG. 5 (d) in which thesupport is shown fully advanced, no re-alignment with the conveyorhaving been required (the element 4 is shown midway between the elements2, 3) the links 95 have their surfaces 98 abutting their respectivebrackets 96 and the cams 102 are just clear of the co-operating secondsurfaces on the bases 5A, 5B. If, however, prior to advance of theelements 2, 3, the conveyor 30 had moved in the direction of the arrowX'then as the elements 2, 3 become freed from lateral restraintor asthey approach the position of freedom from lateral restraint-the surfaceat 103 (FIG. 3) on the base 5B engages and then runs along the surface101 of the link 95 to the cam 102 and as this occurs, the latter isrotated so that its surface 98 moves away from the bracket 96, forexample, to the position shown in full lines in FIG. 3. As this occursthe link 95 exerts a leverage on the base SE to move it in the directionof the arrow X and the greater the disparity between the position of thesupport during its final advancing movement and the position in which itshould be relative to the conveyor the greater is the lever arm 100 andconsequently so is the correcting force to move the support into thedesired predetermined position. It will be appreciated that due to themovement of the conveyor 30 the ram 35 of the support and of adjacentsupports will also receive a corresponding movement so that the links95, of adjacent supports (see FIG. 3) are liable to approach and mayoverlap and/or foul one another. The vertical surfaces 104 are providedto prevent this occurring.

Movement of the conveyor 30 may occur, for example, in the direction ofthe arrow X, due to passage of a coal cutting machine when the elements2, 3 are in the advanced position adjacent to the conveyor 30. In thisposition the rams 35, 36 may be vented and as the conveyor moves thelink 95 pivots about the cam 102 which abuts the co-operating surface onthe base 5B and in consequence the ram 36 is extended a small amountthus permitting the movement of the conveyor to take place withoutdamage to the support.

It will be observed that the link 95 is so formed that during the finaladvancing movement of the support, the cam 102 is positioned so that itis enabled to engage the co-operating second surface at 103 a shortdistance, for example, 4 to 6 inches, before the support reaches itsfully advanced position enabling the support to be guided or steeredinto its predetermined position relative to the conveyor even though thesupport may not be fully advanced.

Although this invention has been described with refer ence to aparticular construction of two part support which includes an adjacentroof support member which is contained by the other part of the supporti.e. a sup port having two interconnected roof support elements with athird independent roof support element therevbetween, it will beappreciated that the restraint may equally well be applied by adjacentsupports on either side of a support which is being advanced to theconveyor. This differentiates from previous proposals which guide anadvancing support relative to the anchorage only or relative to anadjacent support or supports only, neither of which arrangements hasbeen found to be entirely satisfactory in practice.

We claim:

1. A mine roof support comprising at least two roof support elements;means connecting said roof support elements for simultaneous advancingmovement, each of said elements comprising a base, a roof bar and atleast one extensible prop arranged therebetween; two advancing rams;means connecting said rams one to each of said elements, said rams beingadapted for pivotal connection to an anchorage; first guide surfacescarried by said two elements; at least one adjacent support element;complementary guide surfaces on said one adjacent support element, saidfirst guide surfaces being arranged to cooperate with said complementaryguide surfaces whereby on closure of said rams to advance said roofsupport, said first guide surfaces and said complementary guide surfacesguide said roof support relatively to said at least one adjacent supportelement over a substantial part of the support advancing stroke of saidrams, engagement of said cooperating guide surfaces restraining said atleast two support elements from lateral movement, and the restraintimposed by said cooperating guide surfaces being removed over the finaladvancing movement of the support so as then to permit lateral movementthereof.

2. A mine roof support comprising two roof support elements; meansconnecting said roof support elements for simultaneous advancingmovement, each element comprising a base, a roof bar and at least oneextensible prop arranged therebetween; two advancing rams; meansconnecting said rams one to each of said elements, said rams beingadapted for pivotal connection to an anchorage; first guide surfacescarried by said two elements; an independently moveable roof supportmember arranged between and laterally spaced from said roof supportelements; complementary guide surfaces on said independently moveableroof supporting member, said first guide surfaces being arranged tocooperate with said complementary guide surfaces whereby, on closure ofsaid rams to advance said roof support, said first guide surfaces andcomplementary guide surfaces guide said roof support relatively to saidindependently moveable roof supporting member over a substantial part ofthe support advancing stroke of said rams, engagement of saidcooperating guide surfaces restraining said two support elements fromlateral movement, and the restraint imposed by said cooperating guidesurfaces being removed over the final advancing movement of the supportso as then to permit lateral movement thereof.

3. A mine roof support as claimed in claim 2, including second surfaceson the support; link members, one pivotally connected to each advancingram and adapted for pivotal connection to the anchorage; and a secondguide surface on each link member arranged to cooperate with said secondsurfaces on the support so as, on closure of the rams, to guide thesupport into a predetermined position relative to the anchorage, thelink members being so formed and the pivotal connections being soarranged that, when the support approaches its fully advanced position,the axis of each ram is inclined to a line joining the pivotalconnection at the anchorage and the support, whereby a leverage isexerted on the link members tending to exert a lateral force on thesupport so as to steer it into a predetermined position relative to theanchorage or restrain it from moving away from that position.

4. A mine roof support as claimed in claim 3, in which the first guidesurfaces comprise forward and rear sections providing discontinuousguide surfaces.

5. A mine roof support as claimed in claim 3, in which the link membersinclude cam portions adapted to engage the support and transmit alateral force thereto and further comprise generally vertical plateportions adapted to prevent overlapping of the link members with thelink members of adjacent supports.

6. A mine roof support as claimed in claim 1, said one adjacent supportelement comprising a third roof supporting element, said complementaryfirst surfaces being provided on said third roof supporting element, thethird element comprising a base, a roof bar and two eX- tensible propsarranged therebetween, the third element having lateral clearance fromand being located between said first two elements; a third advancing rampivotally connected between said third element and the first twoelements; and means to permit relative vertical and lateral movementbetween the third element and the first and second elements.

7. A mine roof support as claimed in claim 6, in which the first guidesurfaces comprise forward and rear sections providing discontinuousguide surfaces, the first and second advancing rams being double acting;a link member pivotally connected to each of the first and secondadvancing rams and being adapted for pivotal connection to the achorage;abutment surfaces on the link members adapted to engage the anchoragewhereby, on extension of said rams, force is transmitted to saidanchorage to move it away from said support; cam portions on the linkmembers adapted to engage the support and transmit a lateral forcethereto during closure of the rams; and generally vertical plateportions on the link members adapted to prevent overlapping of the linkmembers with the link members of adjacent supports.

8. A mine roof support comprising a pair of support elements; meansconnecting said pair of support elements for simultaneous advancingmovement, each element comprising a base, a roof bar and at least oneextensible prop arranged therebetween; two advancing rams; meansconnecting said rams, one to each of said elements of said pair, saidrams being adapted for pivotal connection to an anchorage; first guidesurfaces carried by the pair of elements; an adjacent support element oneach side of said pair of support elements; complementary guide surfaceson said adjacent support elements, said first guide surfaces beingarranged to cooperate with said complementary guide surfaces whereby, onclosure of said rams to advance said roof support, said first guidesurfaces and complementary guide surfaces guide said roof supportrelatively to adjacent roof supporting members over a substantial partof the support advancing stroke of the rams, engagement of saidcooperating guide surfaces restraining said two support elements fromlateral movement, and in which the restraint imposed by said cooperatingguide surfaces is removed over the final advancing movement of thesupport so as then to permit lateral movement thereof; second surfaceson said support; link members, one pivotally connected to each advancingram and adapted for pivotal connection to the anchorage; and a secondguide surface on each link member arranged to cooperate with said secondsurfaces on the support so as, on closure of the rams, to guide thesupport into a predetermined position relative to the anchorage, thelink members being so formed and the pivotal connections being soarranged that, when the support approaches is fully advanced position,the axis of each ram is inclined to a line joining the pivotalconnection at the anchorage and the support, whereby a leverage isexerted on the link members tending to exert a lateral force on thesupport so as to steer it into a predetermined 9 10 position relative tothe anchorage or restrain it from mov- FOREIGN PATENTS mg away fmm that1,026,965 4/1966 Great Britain.

References Cited 1,044,907 10/1966 Great Brltaln.

UNITED STATES PATENTS 5 DENNIS L. TAYLOR, Primary Examiner 2,644,3117/1953 Malloy 61--45 3,333,426 8/1967 Jackson 61-45 248 357 3,355,89812/1967 Barrett et a1. 6145 3,425,229 2/1969 Groetschel 61-45

